Vortex resonance wind turbine

ABSTRACT

Wind turbine consisting of an anchoring to the ground or to a base and a mast, the natural oscillation frequency of which is purposely adjusted to the frequency of appearance of the air vortices or eddies produced after the collision of a laminar and stationary airflow against the surface thereof. The aeroelastic energy thus absorbed is converted into electrical energy due to the use of materials with high electromechanical coupling.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/811,788, filed Jan. 23, 2013, which is a national stageapplication under 35 U.S.C. §371 of PCT/ES2011/000252, filed Aug. 1,2011, which claims priority to Spanish Patent Application P201001003,filed Aug. 2, 2010, the contents of each of which are incorporated byreference herein.

OBJECT OF THE INVENTION

The present invention relates to a new instrument for generatingelectrical energy.

The object of the invention consists of a generating device belonging tothe renewable energy industry, transforming wind energy into usableelectric potential. Its design integrates three known physicalprinciples: structural coupling to the natural frequency of oscillation,the generation of vortices in fluids, and the electromechanical couplingof some materials, for example due to the ferroelectric effect or thepiezoelectric effect.

The novelty of this system resides in the coordinated integration ofthese three principles in an electrical energy generation device thattunes its natural oscillation frequency to the generation frequency ofvortices that are generated in a synchronised manner throughout thestructure.

BACKGROUND OF THE INVENTION

One of the most widespread forms of renewable energy is wind power,which relies on wind as the primary energy source.

The devices most commonly used to transform wind energy into electricityare multi-blade wind turbines. Despite the clear and undeniabletechnological improvements continuously achieved, these systems sufferfrom four fundamental drawbacks:

a) As they have mechanical components, gears, coils, etc. they havemaintenance costs due to consumption of lubricants, part wear, heatdegradation of insulating resins and other effects related to friction,heating due to friction, etc.

b) Conventional multi-blade wind turbines, based on theoretical workperformed by Betz in 1927, increase their efficiency the higher therotation speed of the rotors. This, in conjunction with the fact thatthe amount of energy available in a circular surface increases with thesquare of the blade length, means that the speed at the tips of theblades is very high, representing a high risk to avian fauna, withnumerous accidents having been recorded.

c) The deliberate increase in size translates into a substantialincrease in the complexity of its assembly, increasing initialinstallation costs.

d) The subjective visual impact of wind turbines can be described inmany ways, but in any case their presence is accentuated by their widerange of motion.

In order to improve these aspects, the present invention describes adevice based on three physical principals or fundamentals. Theseprinciples are widely used separately in the industry:

The first principle is electromechanical coupling. This effect isexhibited by certain materials in which when a force is applied betweentwo of their faces a potential difference is created between them. Aswith any electrical machine, its operation is reversible and thepresence of a voltage between two of its faces causes a deformation.Among these materials are ferroelectric materials (such as leadzirconate titanate and its derivatives) and piezoelectric materials(certain crystals such as quartz, etc.).

Materials with some type of electromechanical coupling have a wide rangeof applications as actuators (positioners, motors), speakers(introducing electrical energy and obtaining mechanical energy) and assensors for pressure, position, contact, deformation and transducers ofvarious types (in which mechanical energy is introduced to obtainelectrical energy).

Their application in the generation of electrical energy is not sowidespread, but there already exist pavements and floors walked on bypedestrians that transform the energy of their steps into usableelectrical energy. There are proposals for clothing, footwear and evensilicone implants that obtain energy from the movement of the body anduse it to recharge portable electronic devices. They have been used forsome time in electric arc lighters to produce the lighting spark inlighters, keyboards that recharge the device that they are included inwith the user's keystrokes, etc. Similarly, there are designs for anelectricity generator that intends to gather the pulsing and turbulentenergy from the impact of waves or wind.

A second principle is the deliberate generation of turbulent vorticesfrom a non-turbulent laminar flow. The ‘Karman vortex street’ wasdescribed by the Hungarian scientist Theodore von Karman in 1911, andits most used technological application is a specific type of flowmeterknown as a vortex flowmeter, which measures the amount of fluid passingthrough a duct by counting the number of vortices formed inside it dueto the presence of an element with a known geometry. The knowledge andmodelling of this principle is also used in atmospheric and oceanicforecasting.

The third principle relates to the natural oscillation frequency ofbodies. It is applied intentionally in the manufacture of musicalinstruments, loudspeakers, electronic devices (resonators), in someapplications in microscopy (“tapping” in AFM, MRFM, and othermicroscopes, which have a cantilever that oscillates harmonically toimprove the reading from the tip), etc. On the other hand, it is aneffect that is avoided if possible in other technological areas, such asautomotion and mechanics (Structural Acoustic Coupling Control) toreduce noise in engines, in brake pads, etc. It is also an undesiredeffect in architecture and large structures, such as smokestacks orbridges (as in the famous and exemplary case of the Tacoma Narrowsbridge or the Ferrybridge Power Station cooling towers, where theaforementioned Karman vortices were also generated), etc.

No wind turbine generator device has been found which, in its geometry,intentionally seeks to synchronise the appearance of the turbulentvortices that appear throughout its structure.

No electrical generator has been found to date that purposely seeks thenatural oscillation of bodies as an operational principle. Noneestablishes in a controlled manner tuning or resonance of any typebetween their natural oscillation frequency and the frequency at whichturbulent vortices are generated.

No electrical generator of those based on materials withelectromechanical coupling has been found to date that uses as itsprimary energy source the energy contained in a stationary laminarairflow.

DESCRIPTION OF THE INVENTION

The vortex resonance wind turbine disclosed herein is a solution to theproblems caused by conventional multi-blade wind turbines that have beendescribed previously.

The vortex resonance wind turbine consists of a vertical, semirigiddevice anchored to the surface of the ground. The more visible part is avertical block or mast which, as it has no moving parts (reducers,gears, axles, rotors, etc.) does not require lubrication or change ofparts due to wear or fatigue. It is manufactured in part or in fullusing materials with a high electromechanical coupling.

Under certain wind conditions (speed, Reynolds number, etc.), the windstriking its surface causes a series of turbulent vortices or eddiesdownstream that transmit two types of force to its structure. One force,known as drag, is in the same direction as the wind and in case oflaminar and stationary airflow causes a torsion fixed in time(non-usable force) and another force, known as lift, is perpendicular tothe wind direction and the sense of which changes its sign alternately,maintaining its direction constant (usable force). If we have a laminarand stationary flow, the frequency with which this force changes sensedue to the appearance of new vortices is described by Karman's formula:

${Fv} = \frac{S \cdot V}{h}$

Where F_(v) is the frequency of appearance of vortices, V is the airspeed, h is the characteristic length of the geometry of the obstacle(for example the diameter for one with a circular cross section) and Sis the adimensional Strouhal number for the fluid.

As with any solid element or structure, the device object of theinvention has several spatial oscillation modes. For a mast anchored tothe ground on one end, the first oscillation mode is that in which oneend is static and the opposite end, the highest, has maximum amplitude.The value of its frequency is given by:

$f_{n} = {\frac{1}{2\; \pi} \cdot \sqrt{{\frac{IE}{d_{l}} \cdot K_{n}^{4}} - a^{2}}}$

Where f_(n) is the natural oscillation frequency for the nth harmonic, Iis the sectional moment of inertia, E is the Young's modulus of thematerial, d_(I) is the density of the bar per unit length, K_(n) is thenth oscillation mode of the bar and a is a damping constant.

If the natural oscillation frequency of the mast f_(n) is the same asthe frequency F_(v) at which it itself generates the vortices in theair, the structure and the turbulent regime will be in tune, and theassembly will resonate, thereby maximizing its capacity for energyabsorption. This tuning of the natural oscillation frequency and thevortex generation frequency can be dangerous in certain structures suchas bridges or smokestacks, but in our case it is the desired goal.

Materials with electromechanical coupling obtain a highly variableefficiency in the energy transformation process depending on the qualityof the material. At present it is difficult to find materials withefficiency greater than 75% as there is always a significant amount ofenergy that is transformed into elastic potential energy. In theresonance case (when the material oscillates at its natural oscillationfrequency) a substantial part of this elastic potential energy isrecovered and the efficiency is closer to 100%. In this way, if in ourcase the mast or an object attached to it has pronouncedelectromechanical coupling (whether ferroelectric or piezoelectric), thetransformation of mechanical energy into electrical energy is optimised.

As discussed above, the frequency of oscillation of a body depends onits density, its cross-sectional moment of inertia and its elasticrigidity constant or Young's modulus. As the frequency of appearance ofthe vortices depends on the air speed (which is not controlled and canvary over time), in order to tune or match the two frequencies (naturaloscillation and vortex generation frequencies), it is possible to modifyany of the control parameters on which the natural frequency ofoscillation of the mast depends, and preferably to others the Young'smodulus. This can be achieved by externally modulating the voltage towhich are subjected the materials with electromechanical coupling thatmake them up. For this purpose, the vortex resonance wind turbine has anelectronic unit meant to manage a control loop where the output is thevalue of the voltage to which are subjected the materials withelectromechanical coupling and the input is the wind velocity. Thisvalue can be obtained by a standard wind gauge, or even better by usingthe stationary torsion of the wind turbine mast generated by the dragforce. Another of its purposes is to filter and condition the energygenerated by the device before it is supplied to the subsequentinversion and filtering stages that will allow it to be fed to the powergrid.

The most natural location for the electronic control and regulation unitwill be one where it does not interfere with the natural airflow.

Anchoring to the ground is established by a solid foundation or base ofa typical binding agent such as concrete, cement, plaster, or mortar. Itmust be heavy and provide a firm and stable anchoring to the ground.

As stated above, the optimum operation of the vortex resonance windturbine requires a laminar and stationary airflow to strike it. It isknown that closeness to the ground produces turbulent regimes, so that ahigh mast is advisable. In addition, the energy contained in the wind isproportional to its speed to the power of 3. This results in the need toincrease the height of the mast.

It is obvious that for a correct operation of the device, the mast mustreceive the lift forces in all of its segments (at any height) in asynchronised manner and thereby oscillate. Hellman's exponential lawexpresses the increase in speed with the distance from the ground:

$V_{z} = {V_{h} \cdot \left( \frac{z}{h} \right)^{p}}$

Where z is the height at which the air speed needs to be known, h is theheight at which the air speed is known and V_(z) and V_(h) arerespectively the unknown and known air speeds.

As the vortex generation frequency depends on air speed, Hellmann'sexponential law and Karman's formula must be introduced in its geometryincreasing its diameter as a function of the expected air speed, thatis, adjusting its diameter with the height.

This new wind turbine system can be used in areas that can be exploitedby conventional systems and, due to its characteristics, can be used inareas (urban and industrial) generally forbidden for traditional windturbines.

Given its structural simplicity, the transport, storage and installationof the device is very simple, particularly when compared to installationrequirements for conventional wind turbines. In fact, if the windgeneration industry is currently capable of installing large turbines,there is no reason why with similar or fewer means it would not bepossible to install vortex resonance wind turbines of equal or greaterdimensions.

DESCRIPTION OF THE DRAWINGS

To complete the description being made and in order to aid a betterunderstanding of the characteristics of the invention, according to anexample of a preferred embodiment thereof, a set of drawings is enclosedforming an integral part of the description where, for purposes ofillustration and in a non-limiting sense, the following is shown:

FIG. 1 shows a schematic representation of a cross-sectional elevationview corresponding to the vortex resonance wind turbine.

FIG. 2 shows a graph representing, by way of example, the variation inthe thickness of the mast with its height (according to Hellmann'sexponential law and Karman's formula). As in this case the cross sectionis circular, the radius R in meters is specified versus the height H,also in meters.

FIG. 3 shows a schematic representation of the “Karman vortex street”and the forces due to this effect on the surface that generates it.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the wind turbine object of the invention isdescribed below with reference to the figures.

The vortex resonance wind turbine has no gears, bearings, etc., so thatits assembly consists of placing the components that are physicallyconnected in the described position and with physical or electricalcontact between them.

A hole is made on the ground (12) large enough to receive the base (1)of cement or concrete, as in the foundations of any building orstructure. The bottom of the mast (4) is attached to the base (1) at ananchoring area (5) allowing the higher part of the mast (4) to oscillatefreely with no other constraint that the elasticity of the material.From an electrical point of view the mast (4), formed by elements with ahigh electromechanical coupling (13), is connected to the electronicunit for control and regulation (3) located in the sealed compartment(2) provided in the base (1) for this purpose. This connection isestablished by electrical conductors (7) introduced through a passage orduct (6) also made in the base (1). Connection to the power grid of theinstallation (8) is established with connection cables (9) that will berouted in a ditch made in the ground (12) and which leave the base (1)through sealed plugs (10). Access to the sealed compartment (2) isgained through a cover (11) that provides access to its interior andallows assembly and maintenance actions to be carried out.

To define dimensional aspects and considering that the mast (4) has acircular cross section (15) to avoid depending on wind direction and avariable radius R as a function of the height H, FIG. 2 shows a graphindicating that for a mast with a height of 4 meters and a desirednatural oscillation frequency, for example, of 8 Hertz (determined amongother factors by the Young's modulus of the material with which it ismade), the cross section (15) changes from a radius of 82.9 mm at aheight of 1 meter from the ground (12) to 105.3 mm at 4 meters. Thisgeometry produces a synchronised appearance of vortices along the entirelength of the mast (4) for a wind governed by a Hellman's exponentialcoefficient of p=0.16 and a mean air speed of 6.5 m/s at a height of 10meters.

As regards the fluid, the laminar and stationary wind (14) strikes themast (4) producing a drag force (18) that cannot be used and a liftforce (19) with a sense and magnitude that changes over time. Any of thepossible circular cross sections (15) of the mast (4) with a planeperpendicular to its main axis will generate a series of alternatingvortices (16) which, in the stationary case, travel between them at aconstant distance (17). The lift forces (19) are caused by thesevortices (16). If the wind direction changes, the control and regulationunit (3) will actively modulate the Young's modulus of the mast (4),changing the electrical voltage affecting the elements with a highelectromechanical coupling (13) that conform it, thereby tuning itsnatural oscillation frequency with the appearance of the vortices (16).

The power grid of the installation (8) receives the energy supplied byone or more vortex resonance wind turbines and can be equipotential(direct current). It is in charge of sending all this energy to anelectrical substation that will transform and condition it according tothe requirements of the utility company or station received saidelectrical energy.

There are only a few requirements for the distribution of the windturbines on the ground. In addition to a correct anchoring to theground, the aerodynamic interference between them must be minimised,separating them to improve their efficiency.

To reduce their visual impact, the vortex resonance wind turbines canhave a colour that makes them blend in with the surroundings, althoughin a preferred embodiment refractory paint (white, silver, etc.) is usedto reduce the degradation caused by sunlight.

1.-4. (canceled)
 5. A vortex resonance wind power generator, comprising:a mast for capturing wind energy, the mast having one end attached to abase and a higher part capable of oscillating freely, the mast beingarranged so that stationary and laminar airflow striking the mast istransformed into a turbulent flow, forming vortices or eddies, the masthaving a cross section with a characteristic dimension that increases ina longitudinal direction as a function of the height, to produce asynchronized appearance of vortices along the mast.
 6. The vortexresonance wind power generator according to claim 5, wherein the masthas a circular cross section with a diameter, the characteristicdimension being the diameter.
 7. The vortex resonance wind powergenerator according to claim 5, wherein the mast has a height of morethan 1 meter.
 8. The vortex resonance wind power generator according toclaim 5, wherein the mast has a height of more than 4 meters.
 9. Thevortex resonance wind power generator according to claim 5, furthercomprising means for modulating the natural frequency of oscillation ofthe mast to match or tune it to the frequency of appearance of vortices.10. The vortex resonance wind power generator according to claim 6,further comprising means for modulating the natural frequency ofoscillation of the mast to match or tune it to the frequency ofappearance of vortices.
 11. The vortex resonance wind power generatoraccording to claim 7, further comprising means for modulating thenatural frequency of oscillation of the mast to match or tune it to thefrequency of appearance of vortices.
 12. The vortex resonance wind powergenerator according to claim 5, wherein the characteristic dimensionincreases in the longitudinal direction from a bottom of the mast towarda top of the mast, as a function of the height thereof.
 13. The vortexresonance wind power generator according to claim 5, wherein at an upperend of the mast, the characteristic dimension decreases in thelongitudinal direction toward a top of the mast, as a function of theheight thereof.
 14. The vortex resonance wind power generator accordingto claim 6, wherein at an upper end of the mast, the diameter decreasesin the longitudinal direction toward a top of the mast, as a function ofthe height thereof.
 15. The vortex resonance wind power generatoraccording to claim 5, wherein the characteristic dimension increases inthe longitudinal direction so that the vortices or eddies appear in asynchronized manner along the entire length of the mast.
 16. The vortexresonance wind power generator according to claim 6, wherein thediameter increases in the longitudinal direction so that the vortices oreddies appear in a synchronized manner along the entire length of themast.
 17. The vortex resonance wind power generator according to claim5, wherein the mast comprises elements with a high electromechanicalcoupling for producing electrical energy out of the oscillating movementof the mast.
 18. The vortex resonance wind power generator according toclaim 5, wherein the mast comprises elements with a highelectromechanical coupling for adapting the natural frequency ofoscillation of the mast.
 19. The vortex resonance wind power generatoraccording to claim 5, wherein the characteristic dimension increases ina non-linear manner as a function of the height.
 20. The vortexresonance wind power generator according to claim 6, wherein thediameter increases in a non-linear manner as a function of the height.21. A method of producing electrical energy with a mast having one endattached to a base and an opposite end capable of oscillating freely,comprising: subjecting the mast to wind so that vortices or eddiesappear with a frequency, causing the mast to oscillate; and adapting thenatural frequency of oscillation of the mast to wind speed so that thenatural frequency of oscillation of the mast matches the frequency ofappearance of the vortices.
 22. The method according to claim 21,wherein adapting the natural frequency of oscillation of the mast to thewind speed comprises modulating the Young's modulus of the mast.
 23. Themethod according to claim 21, wherein a characteristic dimension of thecross section of the mast increases in a longitudinal direction as afunction of the height, so that the vortices or eddies appear in asynchronized manner along the entire length of the mast.
 24. The methodaccording to claim 23, wherein the mast has a circular cross section,the characteristic dimension being the diameter of the mast.